Field of the Invention
The present invention relates to an absolute encoder, a processing method, a program, a driving apparatus, and an industrial machine.
Description of the Related Art
Incremental encoders and absolute encoders have been used to measure the position or angle of an object. Absolute encoders can obtain an absolute position by detecting marks corresponding to a sequence of codes, such as maximum length sequence (m-sequence) codes or Gray codes, and thus do not require an origin detecting function for obtaining the absolute position. Incremental encoders having an origin detecting function require origin detection when they cannot accurately measure an absolute position because of, for example, high-speed movement beyond an allowable range. Although absolute encoders do not require origin detection, they may generate an incorrect code sequence due to scratches or dust on the scale or detecting unit. A method described in PCT Japanese Translation Patent Publication No. 2004-529344 is known as a technique used to address such a problem. This method compares a code sequence obtained by detection of marks with each of code sequences in a lookup table prepared in advance, and selects a code sequence having a good match in the lookup table.
The method described in PCT Japanese Translation Patent Publication No. 2004-529344 compares a code sequence obtained by detection with all code sequences in the lookup table. Therefore, if a code sequence having a good match with an incorrect code sequence is selected, an incorrect absolute position may be output. Also, if the total number of code sequences in the lookup table increases with an increase in scale length or a decrease in mark pitch, the time or load required for the comparison may increase.